Heater Pressure Switch Error
Fix FLO, PS, and LO error codes from flow detection problems
Quick Answer
Pressure switch errors (FLO, PS, LO codes) occur when the heater detects insufficient water flow. In 80% of cases, the problem is actual low flow from dirty filters, closed valves, or low pump speed - not a faulty switch. Clean your filter first, ensure all valves are open, and run pump on high speed. If error persists, the pressure switch may need cleaning or replacement.
Understanding Heater Pressure Switches
How Pressure Switches Work
- • Flow detection: Senses water movement through heater
- • Pressure differential: Measures pressure change with flow
- • Safety shutoff: Prevents operation without water
- • Electrical contact: Opens/closes circuit to control
- • Adjustable settings: Calibrated for minimum flow
Why Flow Detection Matters
- • Heat removal: Water carries heat away from exchanger
- • Prevents damage: No flow = instant overheating
- • Efficiency: Proper flow ensures heat transfer
- • Safety: Prevents steam, boiling, explosions
- • Warranty: Required for coverage validity
Critical Safety: Never bypass or jumper a pressure switch. Operating without flow detection can crack heat exchangers, create steam explosions, or cause fires within minutes.
Pressure Switch Error Codes by Brand
Common Error Displays
- FLO: Generic flow error (most brands)
- PS: Pressure switch open
- LO: Low flow detected
- E06: Flow sensor fault (Pentair)
- FLS: Flow switch stuck
- PRS: Pressure switch error (Raypak)
Error Behavior
- • Heater won't start at all
- • Starts then shuts down immediately
- • Intermittent operation
- • Error appears with pump running
- • Clears temporarily then returns
- • Multiple errors displayed
Southlake, Westlake, Grapevine Tip: During spring pollen season, clogged filters cause frequent pressure switch errors. Check filter pressure first before assuming switch failure.
Real Flow Problems (80%) vs. Switch Failure (20%)
Common Flow Restrictions - Check These First!
Filtration Issues:
- ✓ Dirty filter: #1 cause - clean when pressure rises 8-10 PSI
- ✓ Old filter media: Sand channels, cartridge collapsed
- ✓ Undersized filter: Can't handle flow requirements
- ✓ Multiport valve issues: Internal problems restrict flow
Pump & Plumbing:
- ✓ Low pump speed: Variable speed set too low
- ✓ Clogged baskets: Pump/skimmer baskets full
- ✓ Closed valves: Bypass or return valves partially shut
- ✓ Air leaks: Suction side air reduces flow
Quick Test: If error clears when you clean filter or open valves, the pressure switch is working correctly - you had a flow problem.
Actual Pressure Switch Failures
Mechanical Failures:
- • Stuck diaphragm from debris
- • Corroded electrical contacts
- • Cracked switch housing
- • Adjustment screw drift
- • Spring tension loss
Symptoms of Bad Switch:
- • Error with obvious good flow
- • No clicking sound when flow changes
- • Intermittent errors randomly
- • Works after tapping switch
- • Visible damage or leaking
Age Factor: Pressure switches typically last 5-8 years. Frequent cycling from variable speed pumps may shorten lifespan.
DIY Troubleshooting Steps
Step 1: Verify Actual Flow
- Check filter pressure gauge (should be under 25 PSI)
- Feel return jets for strong flow
- Ensure pump is on high speed
- Open all valves completely
- Clean pump and skimmer baskets
Step 2: Basic Switch Tests
- Turn pump off and on - listen for switch click
- Gently tap switch housing with screwdriver handle
- Check for loose wire connections
- Look for corrosion or water damage
- Verify switch is mounted securely
Step 3: Flow Optimization
- Clean filter if pressure is high
- Check for air bubbles in pump
- Verify heater isolation valves are open
- Test with spa mode if available (higher flow)
- Remove any flow restrictions
Success Rate: 80% of pressure switch errors are resolved by cleaning filters and ensuring proper flow. Only 20% require switch replacement.
Pressure Switch Safety Warnings
- •Never bypass or jumper out a pressure switch - severe damage occurs within minutes
- •Do not operate heater if switch is suspected faulty - overheating risk
- •Electrical testing of switches requires proper tools and knowledge
- •Incorrect switch replacement can void warranty and create hazards
- •Low flow operation damages heat exchangers beyond repair
- •Always verify actual water flow before condemning switch
Variable Speed Pump Considerations
Special Issues with VS Pumps
Common Problems:
- • Low speed settings don't meet heater flow requirements
- • Programmed speeds change without heater consideration
- • Ramp-up time too slow for switch activation
- • Energy-saving modes conflict with heating needs
Solutions:
- • Set minimum 2400 RPM for heater operation
- • Program "heater mode" at high speed
- • Use external relay to force high speed
- • Adjust ramp rates for quick flow establishment
Pro Tip: Many VS pump flow errors are solved by creating a dedicated heater speed setting that automatically runs when heat is called for.
Professional Pressure Switch Diagnosis
Verify Actual Water Flow
Confirm water is flowing before troubleshooting switch
⚠️ Warning: Most pressure switch errors are caused by actual low flow, not switch failure
Inspect Pressure Switch Location
Check switch mounting and connections
⚠️ Warning: Never bypass pressure switch - it prevents heater damage from low flow
Test Switch Mechanically
Basic tests to verify switch operation
⚠️ Warning: Electrical testing requires voltmeter and safety knowledge
Clean Sensing Ports
Remove debris that may affect pressure sensing
⚠️ Warning: Some switches have sealed diaphragms that cannot be cleaned
Evaluate Flow Rate Requirements
Ensure system meets heater specifications
⚠️ Warning: Undersized pumps or plumbing cause chronic pressure switch errors
Professional Electrical Testing
Advanced diagnosis and replacement
⚠️ Warning: Incorrect switch replacement can damage heater or create safety hazards
Pressure Switch Error Repair Costs
🔧 DIY Attempt
⚠️ Risks:
- • Misdiagnosing flow problems as switch failures
- • Damaging switch with improper cleaning attempts
- • Creating electrical hazards with connection work
- • Missing underlying flow system problems
- • Voiding warranty with incorrect troubleshooting
👷 Professional Service
✅ Includes:
- • Complete flow system evaluation
- • Pressure switch testing and adjustment
- • Flow rate measurement and optimization
- • Switch cleaning or replacement if needed
- • Pump programming for proper heater flow
- • System validation and warranty
Detailed Cost Breakdown
Item/Service | Low | High |
---|---|---|
Diagnostic service call | $125 | $200 |
Flow system optimization | $150 | $250 |
Pressure switch replacement | $200 | $400 |
Switch adjustment only | $150 | $200 |
VS pump programming | $100 | $150 |
Total Range | $725 | $1200 |
💰 Value Tip: CoOpPools offers transparent pricing with no hidden fees. Our worker-owned model means fair prices and invested service.
Prevention Tips
Maintain Proper Filter Cleaning Schedule
Clean filter when pressure rises 8-10 PSI above clean starting pressure. High filter pressure is the #1 cause of flow errors.
Run Pump at Proper Speed
Ensure pump runs at high speed during heating cycles. Variable speed pumps must deliver 20+ GPM for heater operation.
Annual Flow System Check
Professional inspection of pump performance, filter condition, and plumbing restrictions prevents flow-related shutdowns.
Keep Baskets Clean
Empty pump and skimmer baskets weekly. Clogged baskets restrict flow triggering pressure switch errors.
Monitor System Pressure
Install pressure gauges before and after heater. Early detection of flow problems prevents switch damage.
🏊 Pro Tip: Regular professional maintenance prevents 90% of pool problems.Get your maintenance quote today
This Issue Requires Professional Service
Pressure switch errors prevent heating and often indicate flow problems that can damage equipment. Our technicians diagnose whether you have actual flow issues or switch failure, optimizing your system for reliable heater operation.
Mention "pressure switch errors" when calling for faster service
Related Pool Problems
Heater Error Codes
Often RelatedComplete guide to all heater error codes including FLO/PS
Low Filter Pressure
Often RelatedLow pressure often triggers heater flow errors
Pump Not Priming
Sometimes RelatedPriming issues cause heater flow errors
💡 Did You Know? Pool problems often occur together.heater-pressure-switch-error can lead to or be caused by these related issues. Understanding the connections helps prevent future problems.